1. Field of the Invention
The present invention relates to a portable photographing apparatus that uses power supplies of both an AC adaptor and a battery and to a power switching control method.
2. Description of the Related Art
In recent years, a portable photographing apparatus that can photograph people, scenes, and so forth and record them to an information recording medium (hereinafter this apparatus is referred to as the camcorder, which stands for camera and recorder) has been widespread. When the user uses the camcorder outdoors, he or she uses as its power supply a battery.
When the user uses the camcorder indoors or when the battery's remaining power becomes low, he or she needs to connect the camcorder to an AC adaptor that is connected to an AC outlet.
FIG. 1 shows an example of a power supply switching circuit used for the conventional camcorder. For convenience, FIG. 1 shows only a major circuit structure of the power supply switching circuit. Referring to FIG. 1, a battery 51 and an AC adaptor 52 are connected to a DC-DC converter 56. The DC-DC converter 56 supplies power to each portion of the camcorder. The AC adaptor 52 is connected to an AC outlet of a commercial AC power supply. When both the battery 51 and the AC adaptor 52 have been connected to the camcorder, the AC adaptor 52 is used with a priority over the battery 51 to reduce the power consumption thereof.
A microprocessor 57 controls the power supplied to the camcorder. Hereinafter, the microprocessor 57 is referred to as the microcomputer 57. The microcomputer 57 causes a switch disposed on the battery side, for example an FET switch 54, to be turned on and off. When power is supplied from the battery 51 to the DC-DC converter 56, the FET switch 54 is turned on.
In addition, the microcomputer 57 determines whether or not a plug (not shown) of the AC adaptor 52 has been inserted into the camcorder. When the plug of the AC adaptor 52 has not been inserted into the camcorder, a DC voltage supplied through a pull-up resistor 55 causes the level of a detection port of the microcomputer 57 to become the high level (this level is hereinafter referred to as H).
When the plug of the AC adaptor 52 is inserted into the camcorder, a DC voltage terminal is grounded through the pull-up resistor 55. As a result, the level of the detection port of the microcomputer 57 becomes the low level (hereinafter properly referred to as L). The microcomputer 57 can determine whether or not the plug of the AC adaptor 52 is inserted into the camcorder in such a manner that when the plug of the AC adaptor 52 is pulled out of the camcorder, the level of the detection port of the microcomputer 57 changes from L to H. In such a manner, the microcomputer 57 mechanically determines whether or not the plug of the AC adaptor 52 has been inserted into or pulled out of the camcorder. However, the microcomputer 57 does not determine whether or not power is supplied from the AC adaptor 52 to the camcorder.
The following patent document 1 describes a power supply switching method for an adaptor and an internal power supply having a rechargeable battery.
Patent Document 1: Japanese Patent Laid-Open Publication No. 2000-75970
However, this power supply switching circuit has the following drawback. In this power supply switching circuit, the process of the microcomputer 57 is performed by software. Thus, the FET switch 54 cannot be instantaneously turned on and off. In other words, immediately after the plug of the AC adaptor 52 is pulled out of the camcorder, the FET switch 54 cannot be instantaneously turned on so as to switch the power supply from the AC adaptor 52 to the battery 51.
In addition, the microcomputer 57 does not determine whether or not a plug 53 of the AC adaptor 52 has been inserted into the AC outlet. Thus, even if the plug 53 has not been inserted into the AC outlet, when the DC plug of the AC adaptor 52 is inserted into the camcorder, the power supply for the camcorder is switched to the AC adapter 52 side. As a result, power is not supplied to the camcorder.
FIG. 2A and FIG. 2B show an example of an operation state of a conventional camcorder 62. As shown in FIG. 2A, a display portion 61 of the camcorder 62 displays a picture that the camcorder 62 will photograph. A battery 63 has been attached to the camcorder 62. In addition, a plug 67 of an AC adaptor 64 has been inserted into the camcorder 62. Moreover, a plug 65 of an AC adaptor 64 has been inserted into an AC outlet 66.
When the plug 65 is pulled out of the AC outlet 66, as shown in FIG. 2B, the operation of the camcorder 62 stops. Thus, the display portion 61 displays no picture. Since the plug 67 of the AC adaptor 64 has been inserted into the camcorder 62, a microcomputer of the camcorder 62 selects the AC adaptor side. However, since the plug 65 of the AC adaptor 64 has not been inserted into the AC outlet 66, power is not supplied to the camcorder 62. As a result, the operation of the camcorder 62 stops.
FIG. 3A and FIG. 3B show another operation state of the camcorder 62. As shown in FIG. 3A, the camcorder 62 has only the battery 63. The display portion 61 displays a picture that the camcorder 62 will photograph. When the plug 65 of the AC adaptor 64 has not been connected to the AC outlet 66, if the plug 67 of the AC adaptor 64 is inserted into the camcorder 62, the operation of the camcorder 62 stops and the display portion 61 displays no picture as shown in FIG. 3B. In other words, when the plug 67 of the AC adaptor 64 is inserted into the camcorder 62, the AC adaptor is selected. However, since the plug 65 of the AC adaptor 64 has not been inserted into the AC outlet 66, power is not supplied to the camcorder 62.
FIG. 4A, FIG. 4B, and FIG. 4C show a further operation state of the camcorder 62. As shown in FIG. 4A, the battery 63 has been attached to the camcorder 62. In addition, power has been supplied to the camcorder 62 from the AC adaptor 64 connected to the AC outlet 66. When the plug 67 is pulled out of the camcorder 62 in the state shown in FIG. 4A, the operation of the camcorder 62 instantaneously stops and the display portion 61 displays no picture as shown in FIG. 4B. Thereafter, as shown in FIG. 4C, power is supplied from the battery 63 to the camcorder 62. As a result, the camcorder 62 operates again. However, if this situation occurs in the recording mode, the camcorder 62 does not restore the recording mode.
When the plug 67 is pulled out of the camcorder 62, the microcomputer of the camcorder 62 selects the battery side. However, since the microcomputer cannot instantaneously operate the power supply switching circuit, the operation of the camcorder 62 instantaneously stops. When the battery side is selected and power is supplied from the battery 63 to the camcorder 62, its operation is resumed as shown in FIG. 4C.
The foregoing phenomenon can be prevented when the user takes care about the connection of the plug 67 to the camcorder 62. However, such a phenomenon may occur due to carelessness of another person. For example, when there is another person near the user, the person may catch his or her foot on a cord of the AC adaptor 64 and the plug 65 may be pulled out of the AC outlet 66. In particular, when pictures are recorded on an information recording medium such as an optical disc, since unfinished recording pictures cannot be recorded on the recording medium unlike a tape, a situation of which captured pictures have not been recorded on the recording medium may occur.